1. Field of the Invention
The present invention relates to a Cu-based sintered alloy bearing suitable for use in a motor fuel pump that is reduced in size and operates with a high driving force, and relates to a motor fuel pump therewith.
2. Background Art
An engine that employs, as a fuel, a liquid fuel such as gasoline or gas oil is generally equipped with a motor fuel pump. For example, that having a structure as shown in FIG. 1 is known as a motor fuel pump for a gasoline engine.
This motor fuel pump has a structure such that, in a casing 1, a rotating shaft 2 arranged at both ends of a motor 5 is supported by bearings 3a and 3b and an impeller 4 is inserted at one end of the rotating shaft 2, and a narrow gasoline passage is formed along the outer peripheral surface of the impeller 4, the outer peripheral surface of a motor (armature) 5 and the space (not shown) between the bearings 3a and 3b and the rotating shaft 2. The bearings 3a and 3b are made of various Cu-based sintered alloys.
On rotation of the impeller 4 by the rotation of the motor 5, gasoline is introduced into the casing 1 by the rotation of the impeller 4 and the introduced gasoline is supplied into a separately arranged gasoline engine by passing through the gasoline passage formed along the outer peripheral surface of the impeller 4 and the outer peripheral surface of the motor 5. At this time, a trace amount of a fuel passes through the space between the inner peripheral surface of both bearings 3a and 3b and the outer peripheral surface of the rotating shaft 2 and serves as lubricating oil for sliding the rotating shaft.
With recent remarkable weight reduction and realization of high performance in automobile engines, size reduction has strongly been required for motor fuel pumps used in the engines. In the case of the motor fuel pump having the structure described above, high driving force, that is, high rotating speed, is required to secure sufficient discharging performance and to reduce the size. Under these conditions, higher strength and higher wear resistance are required for bearings.
However, no Cu-based sintered alloy bearings used in a conventional motor fuel pumps have sufficient strength and sufficient wear resistance, and therefore the wear At increases rapidly. Wear is accelerated when a liquid fuel contains sulfur or a compound thereof as impurities, thus resulting in relatively short service life.
To develop a bearing suited for use in a motor fuel pump, the bearing being smaller and operated with a high driving force, the present inventors have performed intensive research. As a result, they have succeeded in the development of a Cu-based sintered alloy bearing and a motor fuel pump described below.
The Cu-based sintered alloy bearing according to the first aspect of the present invention is made of a Cu-based sintered alloy with a composition consisting of, by weight, Ni: 10 to 25%, Zn: 10 to 25%, P: 0.1 to 0.9%, molybdenum disulfide: 0.5 to 5%, and Cu and inevitable impurities as the balance. The Cu-based sintered alloy has a texture from a Cu-P compound and molybdenum disulfide being dispersed in a base material made of a solid solution phase of a Cuxe2x80x94Nixe2x80x94Zn alloy and the porosity thereof is within a range of 5 to 25%.
The Cu-based sintered alloy bearing according to the second aspect of the present invention is made of a Cu-based sintered alloy with a composition consisting of, by weight, Ni: 10 to 25%, Zn: 10 to 25%, P: 0.1 to 0.9%, C: 5% or lower, molybdenum disulfide: 0.5 to 5%, and Cu and inevitable impurities as the balance. The Cu-based sintered alloy has such a texture that a Cuxe2x80x94P compound, free graphite and molybdenum disulfide are dispersed in base material made of a solid solution phase of a Cuxe2x80x94Nixe2x80x94Zn alloy and a porosity is within a range of 5 to 25%.
According to the Cu-based sintered alloy bearing with one of the constitutions described above, a liquid fuel is supplied from the outer peripheral surface of a bearing to the inner peripheral surface of a bearing through pores in the bearing and a fluid lubricating film is formed on the inner peripheral surface of the bearing by this liquid fuel. A frictional resistance applied on a bearing during high-speed rotation of a motor is relieved by this fluid lubricating film. Although the wear resistance is lowered as pores are formed, dispersion of a hard Cuxe2x80x94P compound and MoS2 (or MoS2 and free graphite) that have high lubricity in a base material made of a solid solution phase of a Cuxe2x80x94Nixe2x80x94Zn alloy covers lowering of the wear resistance. Therefore, the Cu-based sintered alloy bearing exhibits excellent wear resistance even under the environment of exposure to a high pressure/high speed flow of a liquid fuel, in cooperation with high strength and excellent corrosion resistance of the Cuxe2x80x94Nixe2x80x94Zn alloy that constitutes the base material. Also the Cu-based sintered alloy exhibits excellent corrosion resistance to a liquid fuel containing sulfur and a compound thereof as impurities.
The motor fuel pump according to the third aspect of the present invention comprises a casing, a rotating shaft arranged in the casing, bearings that rotatably support the rotating shaft to the casing, and an impeller fixed to the rotating shaft, and bearings are Cu-based sintered alloy bearings of the first or second aspect.
According to this motor fuel pump, a long service life can be obtained even at a high rotating speed and size reduction can also be achieved.